Is the name of the filegroup in the current database for which to check table allocation and structural integrity. If not specified, or if 0 is specified, the default is the primary filegroup. Filegroup names must comply with the rules for identifiers.

filegroup_name cannot be a FILESTREAM filegroup.

filegroup_id

Is the filegroup identification (ID) number in the current database for which to check table allocation and structural integrity.

NOINDEX

Specifies that intensive checks of nonclustered indexes for user tables should not be performed. This decreases the overall execution time. NOINDEX does not affect system tables because DBCC CHECKFILEGROUP always checks all system table indexes.

ALL_ERRORMSGS

Displays an unlimited number of errors per object. All error messages are displayed by default. Specifying or omitting this option has no effect.

NO_INFOMSGS

Suppresses all informational messages.

TABLOCK

Causes DBCC CHECKFILEGROUP to obtain locks instead of using an internal database snapshot.

ESTIMATE ONLY

Displays the estimated amount of tempdb space required to run DBCC CHECKFILEGROUP with all the other specified options.

PHYSICAL_ONLY

Limits the checking to the integrity of the physical structure of the page, record headers and the physical structure of B-trees. Designed to provide a small overhead check of the physical consistency of the filegroup, this check can also detect torn pages, and common hardware failures that can compromise data. A full run of DBCC CHECKFILEGROUP may take considerably longer than in earlier versions. This behavior occurs because of the following reasons:

The logical checks are more comprehensive.

Some of the underlying structures to be checked are more complex.

Many new checks have been introduced to include the new features.

Therefore, using the PHYSICAL_ONLY option may cause a much shorter run-time for DBCC CHECKFILEGROUP on large filegroups and is therefore recommended for frequent use on production systems. We still recommend that a full run of DBCC CHECKFILEGROUP be performed periodically. The frequency of these runs depends on factors specific to individual businesses and production environments. PHYSICAL_ONLY always implies NO_INFOMSGS and is not allowed with any one of the repair options.

If a snapshot cannot be created, or the TABLOCK option is specified, DBCC CHECKFILEGROUP acquires locks to obtain the required consistency. In this case, an exclusive database lock is required to perform the allocation checks, and shared table locks are required to perform the table checks. TABLOCK causes DBCC CHECKFILEGROUP to run faster on a database under heavy load, but decreases the concurrency available on the database while DBCC CHECKFILEGROUP is running.

Note

Running DBCC CHECKFILEGROUP against tempdb does not perform any allocation checks and must acquire shared table locks to perform table checks. This is because, for performance reasons, database snapshots are not available on tempdb. This means that the required transactional consistency cannot be obtained.

Checking Objects in Parallel

By default, DBCC CHECKFILEGROUP performs parallel checking of objects. The degree of parallelism is automatically determined by the query processor. The maximum degree of parallelism is configured just like parallel queries. To restrict the maximum number of processors available for DBCC checking, use sp_configure. For more information, see Configure the max degree of parallelism Server Configuration Option.

Nonclustered Indexes on Separate Filegroups

If a nonclustered index in the specified filegroup is associated with a table in another filegroup, the index is not checked because the base table is not available for validation. This is a change in behavior in SQL Server 2005. In earlier versions of SQL Server, the nonclustered index and the base table in the other filegroup are checked. To check both the nonclustered indexes and the base tables, run DBCC CHECKDB.

If a table in the specified filegroup has a nonclustered index in another filegroup, the nonclustered index is not checked because of the following:

The base table structure is not dependent on the structure of a nonclustered index. Nonclustered indexes do not have to be scanned to validate the base table.

The DBCC CHECKFILEGROUP command validates objects only in the specified filegroup.

A clustered index and a table cannot be on different filegroups; therefore, the previous considerations apply only to nonclustered indexes.

Partitioned Tables on Separate Filegroups

In versions of SQL Server 2005 earlier than Service Pack 2 (SP2), DBCC CHECKFILEGROUP checks a partitioned table only if the entire table is on the specified filegroup. If the table is spread across multiple filegroups, the entire table is ignored. In SP2 and higher, when a partitioned table exists on multiple filegroups, DBCC CHECKFILEGROUP checks the partition rowsets that exist on the specified filegroup and ignores the rowsets in the other filegroups. Informational message 2594 indicates the partitions that were not checked. Nonclustered indexes not resident on the specified filegroup are not checked.

Understanding DBCC Error Messages

After the DBCC CHECKFILEGROUP command finishes, a message is written to the SQL Server error log. If the DBCC command successfully executes, the message indicates a successful completion and the amount of time that the command ran. If the DBCC command stops before completing the check because of an error, the message indicates the command was terminated, a state value, and the amount of time the command ran. The following table lists and describes the state values that can be included in the message.

State

Description

0

Error number 8930 was raised. This indicates a metadata corruption that caused the DBCC command to terminate.

1

Error number 8967 was raised. There was an internal DBCC error.

2

A failure occurred during emergency mode database repair.

3

This indicates a metadata corruption that caused the DBCC command to terminate.

4

An assert or access violation was detected.

5

An unknown error occurred that terminated the DBCC command.

Error Reporting

A mini-dump file (SQLDUMPnnnn.txt) is created in the SQL Server LOG directory whenever DBCC CHECKFILEGROUP detects a corruption error. When the Feature Usage data collection and Error Reporting features are enabled for the instance of SQL Server, the file is automatically forwarded to Microsoft. The collected data is used to improve SQL Server functionality.

The dump file contains the results of the DBCC CHECKFILEGROUP command and additional diagnostic output. The file has restricted discretionary access-control lists (DACLs). Access is limited to the SQL Server service account and members of the sysadmin role. By default, the sysadmin role contains all members of the Windows BUILTIN\Administrators group and the local administrator's group. The DBCC command does not fail if the data collection process fails.

Resolving Errors

If any errors are reported by DBCC CHECKFILEGROUP, we recommend restoring the database from the database backup. Note that repair options cannot be specified to DBCC CHECKFILEGROUP.

If no backup exists, running DBCC CHECKDB with a repair option specified corrects the errors reported. The repair option to use is specified at the end of the list if reported errors. Correcting the errors by using the REPAIR_ALLOW_DATA_LOSS option might require that some pages, and therefore data, be deleted.